Implantable devices such as pacemakers or defibrillators include a housing and an attached header. The header includes one or more ports to receive a terminal end of an implantable lead. The header includes connector blocks with contacts that electrically communicate with terminal contacts on the lead. The connector block contacts are electrically connected to feedthroughs which contact electronics within the housing. U.S. Pat. No. 5,076,270 discusses header contacts for an implantable device.